IRDC3898-P1V2

12/8/20111

USER GUIDE FOR IR3898 EVALUATION BOARD1.2Vout

DESCRIPTION

The IR3898 is a synchronous buckconverter, providing a compact, highperformance and flexible solution in a small4mm X 5 mm Power QFN package.

Key features offered by the IR3898 includeinternal Digital Soft Start/Soft Stop, precision0.5Vreference voltage, Power Good,thermal protection, programmable switchingfrequency, Enable input, input under-voltagelockout for proper start-up, enhanced line/load regulation with feed forward, externalfrequency synchronization with smoothclocking, internal LDO and pre-bias start-up.

Output over-current protection function isimplemented by sensing the voltage developedacross the on-resistance of the synchronousMosfet for optimum cost and performance andthe current limit is thermally compensated.

This user guide contains the schematic and billof materials for the IR3898 evaluation board.The guide describes operation and use of theevaluation board itself. Detailed applicationinformation for IR3898 is available in theIR3898 data sheet.

BOARD FEATURES

• Vin = +12V (+ 13.2V Max)•Vout = +1.2V @ 0- 6A

• Fs=600kHz

• L= 1.0uH

• Cin= 3x10uF (ceramic 1206) + 1X330uF (electrolytic)

• Cout=4x22uF (ceramic 0805)

SupIRBuckTM

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A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum of 6A load should beconnected to VOUT+ and VOUT-. The inputs and output connections of the board are listed in Table I.

IR3898 has only one input supply and internal LDO generates Vcc from Vin. If operation with external Vccis required, then R15 can be removed and external Vcc can be applied between Vcc+ and Vcc- pins. Vin pinand Vcc/LDO_Out pins should be shorted together for external Vcc operation.

The output can track voltage at the Vp pin. For this purpose, Vref pin is to be connected to ground (use zeroohm resistor for R21). The value of R14 and R28 can be selected to provide the desired tracking ratiobetween output voltage and the tracking input.

CONNECTIONS and OPERATING INSTRUCTIONS

LAYOUT

The PCB is a 4-layer board (2.23”x2”) using FR4 material. All layers use 2 Oz. copper. The PCBthickness is 0.062”. The IR3898 and other major power components are mounted on the top side of theboard.

Power supply decoupling capacitors, the bootstrap capacitor and feedback components are locatedclose to IR3898. The feedback resistors are connected to the output at the point of regulation and arelocated close to the SupIRBuck IC. To improve efficiency, the circuit board is designed to minimize thelength of the on-board power ground current path.

Table I. Connections

Connection Signal Name

VIN+ Vin (+12V)

VIN- Ground of Vin

Vout+ Vout(+1.2V)

Vout- Ground for Vout

Vcc+ Vcc/ LDO_Out Pin

Vcc- Ground for Vcc input

Enable Enable

PGood Power Good Signal

AGnd Analog ground

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Connection Diagram Vin Gnd Gnd Vout

Enable

VDDQ

Vref

Sync

S-CtrlAGnd

PGood Vsns Vcc+ Vcc-

Top View

Bottom View

Fig. 1: Connection Diagram of IR3899/98/97 Evaluation Boards

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Fig. 2: Board Layout-Top Layer

Fig. 3: Board Layout-Bottom Layer

Single point connection between AGnd and PGnd

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Fig. 5: Board Layout-Mid Layer 2

Fig. 4: Board Layout-Mid Layer 1

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Bill of Materials

Item Qty Part Reference Value Description Manufacturer Part Number

1 1 C1 330uFSMD Electrolytic F size 25V

20% Panasonic EEV-FK1E331P

2 3 C3 C4 C5 10uF1206, 25V, X5R, 20%

TDK C3216X5R1E106M

3 4 C7 C12 C14 C24 0.1uF 0603, 25V, X7R, 10% Murata GRM188R71E104KA01B

4 1 C8 2200pF 0603,50V,X7R Murata GRM188R71H222KA01B

5 1 C11 180pF0603, 50V, NP0, 5% Murata GRM1885C1H181JA01D

6 4 C15 C16 C17 C18 22uF0805, 6.3V, X5R, 20%

TDK C2012X5R0J226M

7 1 C23 2.2uF0603, 16V, X5R, 20%

TDK C1608X5R1C225M

8 1 C26 10nF0603, 25V, X7R, 10%

Murata GRM188R71E103KA01J

9 1 C32 1.0uF0603, 25V, X5R, 10%

Murata GRM188R61E105KA12D

10 1 L1 1.0uH SMD 7.1x6.5x5mm,4.7mΩ TDK SPM6550T-1R0

11 1 R1 2KThick Film, 0603,1/10W,1%

Panasonic ERJ-3EKF2001V

12 2 R2 R11 3.32KThick Film, 0603,1/10W,1%

Panasonic ERJ-3EKF3321V

13 2 R3 R12 2.37KThick Film, 0603,1/10W,1%

Panasonic ERJ-3EKF2371V

14 1 R4 100Thick Film, 0603,1/10W,1%

Panasonic ERJ-3EKF1000V

15 1 R6 20Thick Film, 0603,1/10W,1%

Panasonic ERJ-3EKF20R0V

16 1 R9 39.2KThick Film, 0603,1/10W,1%

Panasonic ERJ-3EKF3922V

17 5 R10 R13 R14 R15 R50 0Thick Film, 0603,1/10W

Panasonic ERJ-3GEY0R00V

18 2 R17 R18 49.9KThick Film, 0603,1/10W,1%

Panasonic ERJ-3EKF4992V

19 1 R19 7.5KThick Film, 0603,1/10W,1%

Panasonic ERJ-3EKF7501V

20 1 U1 IR3898 PQFN 4x5mm IR IR3898MPBF

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TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, no airflow

Fig. 10: Output Voltage Ripple, 6A load Ch2: Vout

Fig. 11: Inductor node at 6A loadCh3:LX

Fig. 8: Start up at 6A Load, Ch1:Vin, Ch2:Vo, Ch3:Vcc, Ch4:PGood

Fig. 7: Start up at 6A LoadCh1:Vin, Ch2:Vo, Ch3:PGood Ch4:Enable

Fig. 9: Start up with 1V Pre Bias , 0A Load, Ch2:Vo

Fig. 12: Short circuit (Hiccup) RecoveryCh2:Vout , Ch4:Iout

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TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, no air flow

Fig. 13: Transient Response, 3A to 6A stepCh2:Vout Ch4-Iout

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TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, no air flow

Fig. 14: Bode Plot at 6A load shows a bandwidth of 110.8KHz and phase margin of 50.5 degrees

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TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, no air flow

Fig (16) Feed Forward for Vin change from 7 to 16V and back to 7V Ch2-Vout Ch4-Vin

Fig (15) Soft start and soft stop using S_Ctrl pin

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Fig.18: Power loss versus load current

Fig.17: Efficiency versus load current

TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, no air flow

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THERMAL IMAGESVin=12.0V, Vo=1.2V, Io=0-6A, Room Temperature, No Air flow

Fig. 19: Thermal Image of the board at 6A loadTest point 1 is IR3898Test point 2 is inductor

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PCB METAL AND COMPONENT PLACEMENTEvaluations have shown that the best overall performance is achieved using the substrate/PCB layout as shown in following figures. PQFN devices should be placed to an accuracy of 0.050mm on both X and Y axes. Self-centering behavior is highly dependent on solders and processes, and experiments should be run to confirm the limits of self-centering on specific processes. For further information, please refer to “SupIRBuck™ Multi-Chip Module (MCM) Power Quad Flat No-Lead (PQFN) Board Mounting Application Note.” (AN1132)

Figure 20: PCB Metal Pad Spacing (all dimensions in mm)

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SOLDER RESIST

IR recommends that the larger Power or Land Area pads are Solder Mask Defined (SMD.) This allows the underlying Copper traces to be as large as possible, which helps in terms of current carrying capability and device cooling capability. When using SMD pads, the underlying copper traces should be at least 0.05mm larger (on each edge) than the Solder Mask window, in order to accommodate any layer to layer misalignment. (i.e. 0.1mm in X & Y.)However, for the smaller Signal type leads around the edge of the device, IR recommends thatthese are Non Solder Mask Defined or Copper Defined. When using NSMD pads,

the Solder Resist Window should be larger than the Copper Pad by at least 0.025mm oneach edge, (i.e. 0.05mm in X&Y,) in order to accommodate any layer tolayer misalignment. Ensure that the solder resist in-between the smaller signal lead areas are atleast 0.15mm wide, due to the high x/y aspect ratio of the solder mask strip.

Figure 21: Solder resist

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STENCIL DESIGN

Figure 22: Stencil Pad Spacing (all dimensions in mm)

Stencils for PQFN can be used with thicknesses of 0.100-0.250mm (0.004-0.010"). Stencils thinner than 0.100mm are unsuitable because they deposit insufficient solder paste to make good solder joints with theground pad; high reductions sometimes create similar problems. Stencils in the range of 0.125mm-0.200mm

(0.005-0.008"), with suitable reductions, give the best results. Evaluations have shown that the best overall performance is achieved using the stencil design shown in following figure. This design is for a stencil thickness of 0.127mm (0.005").The reduction should be adjusted for stencils of other thicknesses.

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IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105TAC Fax: (310) 252-7903

This product has been designed and qualified for the Industrial marketVisit us at www.irf.com for sales contact information

Data and specifications subject to change without notice.12/11

PACKAGE INFORMATION

Figure 23: Package Dimensions